[Lowfer] rx loop copuling

[John Andrews]

Dex,

I've been using series tuning into a step-up transformer for years. The 
turns ratio of the transformer determines the signal level and BW up to 
a point. The 1:2 transformer suggested by J.B. is what I have used when 
exact tuning was difficult, such as with a relay-switched capacitor 
bank. The limit of the step-up is reached when the loop resistance 
equals the stepped-down resistance of the receiver input (assuming the 
feedline is "invisible" -- it won't be at 500 kHz). If the receiver or 
preamp had an actual 50 ohm input resistance, and the loop had a 3 ohm 
resistance, 1:4 would be your limit on the transformer. This would give 
maximum signal and minimum BW. That 400 foot 75 ohm feedline will muck 
things up a bit as you go up in frequency, but should be ignorable at 
137 or 185 kHz.

Using an antenna close to what you describe, series-tuned into a 1:2 
transformer, I was able to log 60 aero beacons by ear at mid-day in July 
at the camp up in Maine. So, it should work.

John, W1TAG

On 11/29/2010 11:12 AM, Dexter McIntyre W4DEX wrote:
> I recently strung up a receive loop about 400 feet from the shack in the
> woods.  I have 75 ohm coax running partially underground with remainder
> on the ground to the antenna.  The  antenna is a single turn of WD-1
> army field wire, two twisted wires connected in parallel.  It's is in a
> delta shape with apex about 45 feet high, horizontal run about 8 feet
> above ground and 125 feet long.  Coax runs to center of horizontal
> section.  So far I have found no way to couple to this loop to make it
> receive worth a darn.  Any suggestion for me to try?
>
> Dex
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